For the purpose of illumination, for instance in residential houses, it has been known for a long time to use incandescent lamps that are supplied by a mains circuit; in Europe, the mains circuit typically carries 230 V AC at 50 Hz. A big problem with incandescent lamps is the fact that they convert only a small portion of the available electrical energy into light energy: much energy is consumed and wasted in the form of heat. Thus, there has been and still is a development towards using more efficient lamps, for instance gas discharge lamps but particularly solid state lamps such as LEDs. It even is desirable to replace incandescent lamps by solid state lamps in an existing situation. Solid state light sources such as LEDs need to be driven by an electronic driver, which receive the mains supply voltage and generate an output lamp current. This may be a separate device, but LED lamp units have conveniently been developed in which the LED light source and electronic driver are integrated. Particularly, the present invention relates to such integrated solid state lamps units capable of replacing existing incandescent lamps.
Incandescent lamps have a nominal rating, for instance 60 Watt, 100 Watt, etc, which corresponds to the lamp current when driven by mains voltage, and which corresponds to a certain amount of light emitted by the lamp. Likewise, LEDs have a nominal rating, corresponding to a nominal lamp current. In some circumstances, it is desirable to be able to reduce the amount of light emitted by the same lamp. For this purpose, dimmers have been developed. For the case of LEDs, the electronic driver has a dim function, in which the output lamp current is regulated. Also, specifically with a view to incandescent lamps, electronic mains dimmers have been developed, operating on the basis of phase cutting. Since phase cutting dimmers are commonly known, a discussion thereof will be omitted here. It is noted that such dimmers can be implemented as wall-mounted dimmers, so that a lamp supply voltage would always be a “dimmed” supply voltage.
A complication exists if a dimmable LED lamp unit is to be coupled to an outlet supplied by such mains dimmer, for instance because a dimmed incandescent lamp is to be replaced by a dimmable LED lamp unit. In a dimmable LED lamp unit, the driver expects to be supplied by normal mains voltage and to receive a control signal indicating the desired dim level, and the driver outputs a regulated lamp current in response to such control signal. Such driver would now receive phase-cut mains voltage as supply. So on the one hand the electronic LED driver needs to function properly when receiving phase-cut mains voltage as supply. On the other hand, the phase-cut mains voltage contains dim information, in the form of the phase angle, relating to the dim level desired by the user, and the electronic LED dimmer needs to be capable to use this information as user control input, to read this dim information, and to regulate the output current for the LED lamp accordingly. Such dimmers are known per se.